1. Field of the Invention
The present invention relates to a window-covering product and more particularly, to a cord lock for window blinds or shades.
2. Description of the Related Art
Traditionally, a conventional cord lock for window blinds or shade includes a box mounted on the top rail of the window blinds or shade, a fixed pulley provided in the box, and a movable driving wheel provided in the box to lock or release a cord such that operation of the cord may control up and down movement of the blinds and also stop movement of the blinds (or a shade).
The conventional box, however, is fixed to a recess on the top rail such that an L-shaped iron plate and screws are incorporated to fix the box on the top rail. This arrangement is complex and makes it difficult for consumers to assemble and disassemble the device. To fix the above drawback, U.S. Pat. Nos. 4,945,970 and 7,117,920 disclose a box that is provided with two retractable locking blocks on opposite sides for engagement with the recess. The locking blocks are pressed inwards to place the box onto the top rail, and while the box is completely placed in the recess of the top rail, the locking blocks will jump out automatically to secure the box to the top rail. However, it is very hard for the removable box, the fixed pulley, and the movable driving wheel to resist the force that the user exerts on the cord and the weight of the cord and the window blinds or shade. As a result, the box may become loosened over time, or even become disengaged with the recess.
Additionally, when the cord is pulled downward or swung to the right or left, it moves the movable driving wheel between a release position, in which the movable driving wheel keeps a distance from the fixed pulley, and a lock position, in which the movable driving wheel touches the fixed pulley. In the release position, the blinds (or the shade) are free to move, and in the lock position, the blinds (or the shade) are secured.
However, while in the lock position, the movable driving wheel only has one point touching the fixed pulley such that it provides insufficient force to secure the cord. As a result, the cord may slip or become loosened from the fixed wheel because of the weight of the blinds or the shade.